"/home/yossef/notes/Su/os2/l3.md"

path: Su/os2/l3.md

- **fileName**: l3
- **Created on**: 2026-01-03 19:58:11

This lecture covers Memory Management, which explains how an
operating system handles and organizes the computer's primary
memory to ensure programs run efficiently.

1. Core Concepts and Background

For a program to run, it must be brought from disk into
main memory and placed within a process. The CPU can only
directly access main memory and its internal registers.

• Registers: Extremely fast storage accessible in one
  CPU clock cycle or less.
• Main Memory: Slower storage that can take many
  CPU cycles to access.
• Cache: A faster memory layer between main memory
  and CPU registers to speed up access.

2. Address Spaces and Mapping

A key concept in memory management is the distinction
between two types of addresses:

• Logical Address (Virtual Address): Generated by
  the CPU during program execution.
• Physical Address: The actual address seen by the
  memory hardware.
• Memory-Management Unit (MMU): A hardware device
  that maps virtual addresses to physical ones.

In an MMU scheme, a relocation register value is added
to every process-generated address to locate it in memory.

3. Dynamic Loading and Swapping

These techniques improve memory efficiency:

• Dynamic Loading: A routine is loaded into memory
  only when it is called, saving memory space.
• Swapping: A process may be temporarily moved from
  memory to a backing store and later restored.

4. Memory Allocation and Fragmentation

Memory allocation often involves holes, which are
free blocks scattered throughout memory.

• Contiguous Allocation: Each process occupies one
  continuous block of memory.
• External Fragmentation: Enough total memory exists,
  but it is broken into noncontiguous pieces.
• Internal Fragmentation: Fixed-size allocation leaves
  unused space within allocated blocks.

5. Paging and Segmentation

Two major noncontiguous memory management techniques:

• Paging: Logical memory is divided into fixed-size
  pages, while physical memory uses frames.
• A page table translates page numbers into frame
  addresses.
• TLB (Translation Look-aside Buffer): A fast hardware
  cache that speeds up address translation.
• Segmentation: Memory is divided into logical units
  like the main program, stack, or symbol table.

Analogy to Solidify Understanding

Memory management is like a library:

• Paging: Every book page is the same size, and the
  library has perfectly fitting shelves.
• Segmentation: The library is divided into sections
  like Science or History, each with different sizes.

mind map

continue:./l4.md
before:./l2.md